The present invention relates to magnetic recording, and more particularly to a method and system for providing a tunneling magnetoresistance recording junction suitable for high areal density magnetic recording.
Tunneling magnetoresistive (xe2x80x9cTMRxe2x80x9d) junctions have recently become of interest for potential use in reading recording media in a magnetoresistive (xe2x80x9cMRxe2x80x9d) head. FIG. 1A depicts diagrams of a conventional TMR sensor 10 as viewed from the side. FIG. 1A depicts the shields first and second shields 24 and 26, first and second gaps 20 and 22, leads 11 and 19, and the TMR sensor 10.
FIG. 1B depicts the conventional TMR sensor 10 as viewed from the side and from an air-bearing surface or magnetic material with which the TMR sensor 10 is being used. In addition to the TMR sensor 10, FIG. 1B depicts leads 11 and 19 and first and second gaps 20 and 22, respectively. Not depicted in FIG. 1B are conventional shields 24 and 26, which partially surround the conventional TMR sensor 10. The conventional TMR sensor 10 includes a conventional antiferromagnetic (xe2x80x9cAFMxe2x80x9d) layer 12, a conventional pinned layer 14, a conventional barrier layer 16, and a conventional free layer 18. The TMR junction for the TMR sensor 10 includes the interfaces between the conventional pinned layer 14, the conventional barrier layer 16 and the conventional free layer 18. Also depicted are portions of gaps 20 and 22 that surround a portion of the TMR sensor 10. The conventional pinned layer 14 and conventional free layer 18 are ferromagnetic. The conventional pinned layer 14 has its magnetization fixed, or pinned, in place because the conventional pinned layer 14 is magnetically coupled to the conventional AFM layer 12. The conventional antiferromagnetic layer 12 is approximately one hundred to three hundred Angstroms thick. The conventional pinned layer 14 is approximately twenty to one hundred Angstroms thick. The conventional barrier layer 16 is typically five to twenty Angstroms thick and the conventional free layer 18 is typically thirty to one hundred Angstroms thick.
The magnetization of the conventional free layer 18 of the TMR sensor 10 is biased in the plane of the page when there is no external magnetic field, but is free to rotate in response to an external magnetic field. The conventional free layer 18 is typically composed of Co, Co90Fe10, or a bilayer of Co90Fe10 and permalloy. The magnetization of the conventional pinned layer 14 is pinned perpendicular to the plane of the page. The conventional pinned layer 14 is typically composed of Co, Fe, or Ni. The conventional barrier layer 16 is typically composed of aluminum oxide (Al2O3).
For the conventional TMR sensor 10 to function, a bias current is driven between the leads 11 and 19, perpendicular to the plane of the layers 12, 14, 16 and 18 of the conventional TMR sensor 10. Thus, the TMR sensor 10 is known as a current perpendicular to the plane (xe2x80x9cCPPxe2x80x9d) junction. The direction of flow of the bias current is depicted by the arrow 24. The MR effect in the conventional TMR sensor 10 is. believed to be due to spin polarized tunneling of electrons between the conventional free layer 18 and the conventional pinned layer 14. Thus, spin polarized electrons tunnel through the conventional barrier layer 16 in order to provide the magnetoresistive effect. When the magnetization of the conventional free layer 18 is parallel or antiparallel to the magnetization of the conventional pinned layer 14, the resistance of the conventional TMR sensor 10 is minimized or maximized, respectively. In addition, the magnetization of the conventional free layer 18 is biased to be. perpendicular to the magnetization of the conventional pinned layer 14 when no external field is applied, as depicted in FIG. 1B. The magnetoresistance, MR, of a MR sensor is the difference between the maximum resistance and the minimum resistance of the MR sensor. The MR ratio of the MR sensor is typically called xcex94R/R, and is typically given as a percent. A typical magnetoresistance of the conventional TMR sensor is approximately twenty percent.
FIG. 1C depicts another conventional TMR sensor 10xe2x80x2. The conventional TMR sensor 10xe2x80x2 is substantially the same as the conventional TMR sensor 10. Consequently, the components of the conventional TMR sensor 10xe2x80x2 are labeled similarly. For example, the conventional free layer is denoted as 18xe2x80x2. However, the conventional pinned layer 14 has been replaced by the conventional hard magnetic layer 14xe2x80x2. The conventional hard magnetic layer has a high coercivity, significantly greater than the tens of Oersteds that could be the coercivity of the conventional free layer 18xe2x80x2. Although not depicted, an AFM layer, such as the AFM layer 12 could be utilized in the TMR sensor 10xe2x80x2 to ensure that the magnetization of the conventional hard magnetic layer 14xe2x80x2 is pinned in the desired direction.
The conventional TMR sensors 10 and 10xe2x80x2 are of interest for MR sensors for high areal density recording applications. Currently, higher recording densities, for example over fifty gigabits (xe2x80x9cGbxe2x80x9d) per square inch, are desired. When the recording density increases, the size of and magnetic field due to the bits decrease. Consequently, the bits provide a lower signal to a read sensor. In order to maintain a sufficiently high signal within a MR read head, the signal from the read sensor for a given magnetic field is desired to be increased. One mechanism for increasing this signal would be to use an MR sensor having an increased MR ratio. The conventional TMR sensors 10 and 10xe2x80x2 can have an MR of approximately twenty percent, which is higher than a conventional giant magnetoresistance (xe2x80x9cGMRxe2x80x9d) sensor having a nonmagnetic conducting layer separating a free layer and a pinned layer. Furthermore, the conventional TMR sensors 10 and 10xe2x80x2 have a smaller thickness than a conventional GMR sensor, allowing for a smaller spacing between shields (not shown). The smaller spacing between shields allows for more effective shielding of bits not desired to be read by the TMR sensor 10. The width of the conventional TMR sensors 10 and 10xe2x80x2, shown is in FIGS. 1B and 1C, can be narrower than a conventional GMR sensor. This also aids in allowing the conventional TMR sensor 10 to read smaller bits at higher recording densities.
Although the conventional TMR sensors 10 and 10xe2x80x2 are of interest for high-density recording applications, one of ordinary skill in the art will readily realize that there are several drawbacks to the conventional TMR sensors 10 and 10xe2x80x2. Some of these drawbacks are due to the area of the conventional TMR sensor 10. In particular, the conventional TMR sensors 10 and 10xe2x80x2 often have a nonuniform bias current and may have a reduced MR ratio due to the large area of the TMR sensors 10 and 10xe2x80x2. The area of the conventional TMR junction includes the area of the interfaces between the conventional pinned layer 14 or conventional hard magnetic layer 14xe2x80x2, the conventional free layer 18 or 18xe2x80x2, respectively, and the conventional barrier layer 16 or 16xe2x80x2, respectively. The junction area is defined by the width of the conventional TMR sensor 10 or 10xe2x80x2, w, depicted in FIGS. 1B and 1C, and the lengths of the conventional TMR sensors 10 and 10xe2x80x2 into the plane of the page depicted in FIGS. 1B and 1C. The length of the conventional TMR sensors 10 and 10xe2x80x2 are determined by the stripe height, h, of the conventional TMR sensor 10 or 10xe2x80x2 as depicted in FIG. 1A. The width w of the conventional TMR sensor 10 or 10xe2x80x2 is determined by the track width (not shown) of the media desired to be read and is typically approximately half of the track width. Thus, the junction area for the conventional TMR sensor 10 is the width multiplied by the stripe height (wxc3x97h). The area of the conventional TMR junction for the conventional TMR sensor 10 or 10xe2x80x2 is typically on the order of one quarter of a square micrometer. As discussed above, the conventional barrier layer 16 or 16xe2x80x2 is typically between five and twenty Angstroms thick. Because the conventional barrier layer 16 or 16xe2x80x2 has such a large area but is so thin, pinholes (not shown in FIGS. 1A-1C) often exist in the conventional barrier layer 16 or 16xe2x80x2. Current more easily flows between the conventional pinned layer 14 or the conventional hard magnetic layer 14xe2x80x2 and the conventional free layer 18 or 18xe2x80x2, respectively, through these pinholes than through the conventional barrier layer 16 or 16xe2x80x2, respectively. As a result, the bias current between the leads 11 and 19 or the leads 11xe2x80x2 and 19xe2x80x2 is nonuniform. In addition, because electrons pass readily through these pinholes, the electrons do not undergo spin polarized tunneling. As a result, the MR effect for the conventional TMR sensors 10 and 10xe2x80x2 can be reduced by the electrons which pass through the pinholes instead of tunneling through the conventional barrier layers 16 and 16xe2x80x2, respectively. Consequently, not only may the bias current lack uniformity, but the MR ratios for the conventional TMR sensors 10 and 10xe2x80x2 may also be reduced below the intrinsic percentage (approximately twenty percent).
There are further drawbacks to use of the conventional TMR sensors 10 and 10xe2x80x2. The conventional free layers 18 and 18xe2x80x2, the conventional barrier layers 16 and 16xe2x80x2, respectively, and the conventional pinned layer 14 and the conventional hard magnetic layer 14xe2x80x2, respectively, are two metallic layers separated by an insulating layer. As a result, the conventional free layers 18 and 18xe2x80x2, the conventional barrier layer 16 and 16xe2x80x2, respectively, and the conventional pinned layer 14 and the conventional hard magnetic layer 14xe2x80x2, respectively, form a parasitic capacitor. In part because of the large junction area, the ziiro parasitic capacitances of the conventional TMR sensors 10 and 10xe2x80x2 are relatively large. A parasitic capacitance slows the responses of the conventional TMR sensors 10 and 10xe2x80x2. The characteristic time constant for these delays are proportional to the capacitances of the TMR sensor 10 and 10xe2x80x2. Because the capacitances are larger than desired, the delays are larger than desired. As a result, the responses of the conventional TMR sensor 10 and 10xe2x80x2 are relatively slow and result in slow data transfer rates.
In addition, the conventional TMR sensors 10 and 10xe2x80x2 are fabricated and used in the CPP orientation. Typical conventional GMR. sensor are fabricated such that a bias current can be driven parallel to the plane of the layers of the conventional GMR sensor. In other words, the conventional GMR sensor is fabricated and used in a current in plane (xe2x80x9cCIPxe2x80x9d) configuration. As a result, it may be difficult to fabricate the conventional TMR sensors 10 and 10xe2x80x2 using methods developed for the conventional GMR sensor. As a result, the conventional TMR sensors 10 and 10xe2x80x2 may be relatively difficult to manufacture. Moreover, although the intrinsic MR ratio for the conventional TMR sensors 10 and 10xe2x80x2 are higher than for a conventional GMR sensor, a higher practical MR ratio is still desired.
Furthermore, fabrication of the air-bearing surface (xe2x80x9cABSxe2x80x9d) for the conventional TMR sensors 10 and 10xe2x80x2 may short the conventional TMR sensors 10 and 10xe2x80x2. In particular, the ABS is typically lapped during fabrication. The lapping takes place perpendicular to the plane of the layers in the-conventional TMR sensors 10 and 10xe2x80x2. For example, lapping typically takes-place parallel and antiparallel to the directions of current 24 and 24xe2x80x2 in FIGS. 1A and 1B, respectively. Therefore, the conventional pinned layer 14 and the conventional free layer 18 of the conventional TMR sensor 10, as well as the conventional hard magnetic layer 14xe2x80x2 and the conventional free layer 18xe2x80x2 of the conventional TMR sensor 10xe2x80x2 may be smeared over the conventional barrier layers 16 and 16xe2x80x2, respectively. These magnetic layers 14, 14xe2x80x2, 16 and 16xe2x80x2 are conductive. The smearing of the layers 14, 14xe2x80x2, 16 and 16xe2x80x2 may thus short the conventional TMR sensors 10 and 10xe2x80x2. Consequently, yield is reduced.
With respect to the conventional TMR sensor 10xe2x80x2, there is an additional drawback. The conventional hard magnetic layer 14xe2x80x2 is typically magnetically coupled to the conventional free layer 18xe2x80x2. Because of the small thickness of the conventional barrier layer 16xe2x80x2, this coupling is usually antiferromagnetic in nature. However, the conventional hard magnetic layer 16xe2x80x2 may also be paramagnetically coupled to the conventional free layer 18xe2x80x2. It is also desirable for the conventional free layer 18xe2x80x2 to freely respond to an external magnetic field. Therefore, a magnetic coupling between the free layer 18xe2x80x2 and the conventional hard magnetic layer 14xe2x80x2 greatly reduces the freedom of the free layer 18xe2x80x2 to rotate in response to an external magnetic field such as the field from recording bits, which is undesirable.
When an AFM layer, such as the AFM layer 12, is used with the conventional TMR sensor 10 or 10xe2x80x2, there are additional drawbacks. As the TMR sensors 10 or 10xe2x80x2 are used to read media having a higher areal density, the operating temperature of the device typically increases. Locally, the operating temperature of such devices can be on the order of two hundred to four hundred degrees Celsius, or higher. These operating temperatures are on the order of the blocking temperatures of materials such as IrMn and PtMn, which are typically used for the AFM layer 12. Thus, the AFM layer 12 will lose its ability to pin the conventional pinned layer 14 or the conventional hard magnetic layer 14xe2x80x2 during operation of the device. Moreover, these AFM materials are often corrosive in nature, leading to failures of the conventional TMR junctions 10 and 10xe2x80x2. Furthermore, during manufacturing the conventional TMR sensor 10 or 10xe2x80x2 is heated in order to allow the conventional AFM layer 12 to pin the conventional pinned layer 14 or the conventional hard magnetic layer 14xe2x80x2. The TMR sensor 10 or 10xe2x80x2 is typically heated to a temperature slightly above the blocking temperature of the conventional AFM layer 12, for example between approximately two hundred and four hundred degrees. Heating the entire conventional TMR sensor 10 or 10xe2x80x2 to such a temperature may induce inter-diffusion between the layers of the conventional TMR sensor 10 or 10xe2x80x2, which also can degrade performance.
Accordingly, what is needed is a system and method for providing a manufacturable TMR junction that is capable of being used in high-density magnetic recording. The present invention addresses such a need.
The present invention provides a method and system for providing a magnetoresistive sensor for reading data from a recording media. The method and system comprise providing at least one barrier layer and a free layer having at least one edge. The at least one edge of the free layer is adjacent to the at least one barrier layer. The free layer is ferromagnetic and has a free layer coercivity. The method and system also comprise providing at least one hard magnetic layer. The at least one hard magnetic layer has a coercivity greater than the free layer coercivity. The at least one barrier layer is disposed between the at least one hard magnetic layer and the free layer. The at least one barrier layer is sufficiently thin to allow tunneling of charge carriers between the at least one hard magnetic layer and the free layer.
According to the system and method disclosed herein, the present invention provides a magnetoresistive sensor that has a higher magnetoresistive ratio, is relatively simple to fabricate, which is less subject to nonuniform bias current, does not require an antiferromagnetic inning layer and which is suitable for high areal density recording applications.